The present invention relates generally to the field of medical diagnostic systems employing x-ray tubes as sources of radiation. More particularly, the invention relates to a technique for predicting future life and possible failure of an x-ray tube through analysis of predictive parameters sensed during use of the tube.
A variety of medical diagnostic and other systems are known in which x-ray tubes are employed as a source of radiation. In medical imaging systems, for example, x-ray tubes are used in both x-ray systems and computer tomography (CT) systems as a source of x-ray radiation. The radiation is emitted in response to control signals during examination or imaging sequences. The radiation traverses a subject of interest, such as a human patient, and a portion of the radiation impacts a detector or a photographic plate where the image data is collected. In conventional x-ray systems the photographic plate is then developed to produce an image which may be used by a radiologist or attending physician for diagnostic purposes. In digital x-ray systems a photo detector produces signals representative of the amount or intensity of radiation impacting discrete pixel regions of a detector surface. In CT systems a detector array, including a series of detector elements, produces similar signals through various positions as a gantry is displaced around a patient.
Depending upon the particular modality of the imaging system and the system configuration, the x-ray tube source may be mounted in various manners. For example, in conventional x-ray systems, anode and cathode assemblies support the x-ray tube within a casing. The anode assembly is coupled to a target within a glass or metal envelope, while the cathode assembly is coupled to a cathode plate. A metal shield or casing surrounds the glass envelope. The volume between the casing and the envelope is filled with a cooling medium, such as oil. A window is provided in the casing for emitting x-rays created by controlled discharges between the cathode plate and the target.
The x-ray tube is typically operated in cycles including periods in which x-rays are generated interleaved with periods in which the x-ray source is allowed to cool. A typical imaging sequence may include a number of such sequences. Moreover, the x-ray tube may have a useful life over a large number of examination sequences, and must generally be available for examination sequences upon demand in a medical care facility.
Given the demanding schedules to which x-ray tubes are often subjected, failure of the tubes is of particular concern. Various failure modes have been observed in x-ray tubes, and these may have a variety of sources. For example, within the glass encasement a vacuum or near vacuum is preferably maintained. However, due to leaks, degradation in the cathode or anode materials, decomposition of anode filaments, and so forth, particulates may be created or freed within the tube. These particulates may result in eventual failure of the tubes over time. Failure of the tubes can also be a function of the modes of operation and user-selected parameters, such as voltage or current.
Due to the stringent requirements and reliability demands placed on x-ray tubes in medical diagnostic systems, special programs may be implemented for insuring rapid replacement of the tubes upon failure. Present procedures for replacement of x-ray tubes in medical diagnostic systems are primarily reactionary. Service personnel generally monitor the performance of the tubes over time and through the various examination sequences. However, the service personnel are often made aware of tube failures only as they occur. When a tube does fail, to insure rapid replacement of failed tubes a conventional response is to expedite shipment of a replacement tube which is then installed by trained service personnel at considerable shipping and handling expense. While the x-ray tubes could be shipped in advance and stored on location or in a centralized service facility, these strategies also require inventory of relatively expensive items, again resulting in additional costs of the service program. Such inventories may also inconveniently occupy valuable storage space at the location.
There is a need, therefore, for an improved technique for predicting possible failure of x-ray tubes in medical diagnostic equipment. There is a particular need for a technique which will accurately predict potential failure, permitting replacement tubes to be shipped or replacement to be scheduled in an orderly fashion prior to the actual tube failure. Such a system could also provide feedback for planning the tube manufacturing and assembly process, as well as feedback to system users for planning the replacement process.
The present invention provides a technique for predicting possible failure of x-ray tubes designed to respond to these needs. The technique may be employed in conjunction with various types of systems employing x-ray tubes as radiation sources. The technique is particularly well suited to predicting failure of x-ray tubes in medical diagnostic equipment, such as conventional and digital x-ray systems, CT systems, and so forth. The technique allows data available from x-ray tube control and monitoring circuits to be analyzed as a leading indicator of future tube failure. In a presently preferred embodiment the parameters are monitored in data sweeps by a centralized service facility. Alternatively, the data may be monitored directly at the diagnostic equipment scanners and the analyses performed locally at the medical facility. Discriminant analysis is performed on certain candidate parameters considered to be leading indicators of tube failure. Based upon the results of the analysis an algorithm is developed for future analysis of operating parameters of the tubes. When a failure is predicted, a replacement tube may be ordered and shipped prior to the predicted failures. The facility in which the tube is installed may also be informed of the scheduled tube replacement, as may field service technicians who will install the replacement tube. The technique also facilitates reporting of the operability of the systems incorporating the tubes to the facility.
Thus, in accordance with one aspect of the invention, a method is provided for predicting failure of an x-ray tube. For such failure prediction, a plurality of operating parameters of the x-ray tube are monitored, and a failure prediction value is derived from the monitored parameters. The failure prediction value is compared to a desired reference value. Based upon the comparison a signal indicative of predicted tube failure is generated. The desired reference value may also be derived from the monitored parameters. Moreover, the parameters may be monitored, the comparison made, and the failure prediction signal generated either at a tube location, or at a remote location, such as at a service center. In a presently preferred embodiment, the parameters monitored in the process include parameters related to anode overcurrent events and to spits occurring within the x-ray tube. The failure prediction value may be derived from the monitored parameters in accordance with an algorithm established by statistical methods, such as discriminant analysis.
The invention also relates to a method for predicting potential failure of x-ray tubes which includes steps of monitoring operating parameters of a population of x-ray tubes, and performing statistical analysis of the monitored parameters. A failure prediction algorithm is then generated from the statistical analysis. The statistical analysis may include discriminant analysis of a range of monitored parameters. The method may include further steps of monitoring operating parameters of at least one x-ray tube and predicting failure of the x-ray tube based upon the monitored parameters and the failure prediction algorithm.
The invention also provides a system for predicting failure of an x-ray tube. The system includes a monitoring circuit coupled to the x-ray tube for monitoring operating parameters indicative of possible failure. The system also includes a failure prediction circuit coupled to the monitoring circuit. The failure prediction circuit executes a failure prediction routine based upon the monitored parameters and generates a failure prediction signal based upon the routine. The failure prediction circuit and the monitoring circuit may be provided at the same or at different locations. In a preferred configuration, the failure prediction circuit is positioned remote from the monitoring circuit, and receives data representative of the monitored parameters via a network connection.